Dispensing of hardenable liquids

ABSTRACT

An enclosed vessel for containing a supply of hardenable liquid to be dispensed together with selectively operable pressurizing means for introducing air into the container to exert a superatmospheric pressure on the surface of said liquid, whereby to discharge such liquid from the container into the atmosphere through a discharge line controlled by a dispensing valve and having an intake end submerged within the liquid. There are provided evacuating means operable during discontinuance of the pressurizing operation to evacuate air from the container whereby to withdraw liquid from the discharge line back into the vessel and, optionally, to maintain a reverse flow of air through the discharge line so that the air is introduced into the liquid at a submerged location to thence bubble upwardly through the liquid. In a modified version, the pressurizing air also is introduced into the vessel at a location beneath the surface of the liquid so that it, too, bubbles up through the liquid.

United States Patent Pauwels et al. Feb. 1, 1972 [54] DISPENSING OFHARDENABLE [57] ABSTRACT LIQUIDS An enclosed vessel for containing asupply of hardenable [72] Inventors; w m pauwels, s thfi ld Mich; liquidto be dispensed together with selectively operable pres- Robert Nystmm,Glastonbury, Conn. surizing means for introducing air into the containerto exert a superatmospheric pressure on the surface of said liquid, [73]Asslgnee: Locme Corporahon Newmgton' whereby to discharge such liquidfrom the container into the [22] Filed: Mar. 25, 1970 atmosphere througha discharge line controlled by a dispensing valve and having an intakeend submerged within [21] Appl' 22456 the liquid. There are providedevacuating means operable during discontinuance of the pressurizingoperation to evacuate [52] US. CL... ..222/1, 222/195, 222/399 air fromthe container whereby to withdraw liquid from the [51] Int. Cl ..B65d83/00 discharge line back into the vessel and, optionally, to maintainField f Se h ..222/ l 394, 396, 397, 399, a reverse flow of air throughthe discharge line so that the air is 222/ 7 4 1 5/329; 26 introducedinto the liquid at a submerged location to thence bubble upwardlythrough the liquid. In a modified version, the [56] References Citedpressurizing air also is introduced into the vessel at a location UNITEDSTATES PATENTS beneath the surface of the liquid so that it, too,bubbles up through the llqllld. 3,395,833 8/1968 Rice ..222/399 XPrimary Examiner-Robert B. Reeves Assistant ExaminerFrancis .I. BartuskaAttorney-Watson, Cole, Grindle & Watson 10 Claims, 2 Drawing FiguresDISPENSING OF HARDENABLE LIQUIDS BACKGROUND OF THE INVENTION Thisinvention comprises a process and apparatus for the dispensing ofhardenable, flowable materials such as sealants, adhesives, gasketingmaterials and coatings. (These flowable materials, ranging from trueNewtonian liquids to thixotropic and pastelike substances, frequentlywill be referred to herein as hardenable liquids). Modern industryrequires improved dispensing devices for liquids of this type,particularly where the devices can be adapted to high-speed productionline techniques. This is particularly true in the area of catalyzed orotherwise hardenable adhesives and sealants; compositions of this typeincreasingly are replacing such conventional materials as mechanicalfasteners and preformed nonfiowable sealants in production lineapplications.

For example, many industries today use two-component epoxy adhesives,RTV" sealants or the technically superior one-component anaerobicadhesives and sealants, such as are disclosed in the US. Pat Nos.2,895,950; 3,043,820; 3,046,262 and 3,218,305 to Krieble; and the US.Pat. No. 3,435,012 to Nordlander. Anaerobic" adhesives and sealants areprecatalyzed acrylate monomers which remain in the unpolymerized stateat room temperature, as long as adequate contact with oxygen ismaintained. However, when isolated from oxygen, as when placed betweenclosely fitting metal parts (e.g., in the threads of a mating nut andbolt), the polymerization process (cure) begins and rapidly converts thesealant or adhesive to a hard, durable polymer.

Anaerobic compositions are considered superior to the epoxy adhesives inthat the components necessary to promote hardening of the compositionmay be mixed, and the mixture stored without fear of changes inviscosity or hardening taking place. They are considered superior to theRTV sealants in that they can be stored in contact with the atmospherewithout concern for gradual hardening taking place. In addition,anaerobic adhesives and sealants do provide reliable and rapid cure atroom temperature, initiated by the mere act of confinement.

In view of the lack of satisfactory application equipment, thehardenable liquids such as those discussed above, commonly are broughtto the production line in small quantities and hand applied, thus makingtheir use considerably more difficult and expensive than if suitableapplication equipment were available. One of the major difficultiesinherent in the dispensing of hardenable, flowable materials fromautomatic application equipment is the fact that applicationconventionally must be to specific, limited locations; hence, thehardenable liquids are dispensed through relatively small nozzles orother such orifices under the control of dispensing valves. To reach thedesired location, the liquids generally are pumped to otherwise conveyedthrough tubes, pipes, etc., to the dispensing orifice. In view of thefact that the liquids are, by their nature, hardenable under certainconditions, the small dispensing openings and the lines and associatedvalves which carry the hardenable composition to the point ofapplication frequently become blocked, rendering the application deviceunusable, and causing considerable inconvenience and lost time due toshutdown of the entire production line.

This problem is accentuated by the fact that production lines generallydo not run continuously during the day. Rest periods, lunch hours, etc.,are taken, and the line frequently is stopped intermittently for minorrepairs, adjustments, shift changes, etc. It is inconvenient to cleanthe flow lines and dispensing nozzles of these devices before each ofthese temporary shutdowns. However, if not so cleaned, by the time theapplicator commences operating again, the hardening of the materials inthe lines and the dispensing orifices frequently has proceeded to thepoint where the applicator has become inoperative.

As a result of the above-described problems, when automatic applicationdevices are used with hardenable liquid compositions, compositions whichharden quite slowly are chosen in an effort to prevent blockage of theapplication equipment. This has had the undesirable effect of greatlyincreasing the hardening time after the material is placed on the partsto be sealed, bonded, coated, etc., requiring slower production ratesand increasing the amount of time for which the parts must be stored topermit adequate hardening to take place. Automatic application deviceswhich avoided these and other problems inherent in the prior art wouldmaterially aid the adaption of hardenable liquids such as adhesives,sealants and coatings, to production line techniques, and would be majorimprovements of great utility.

SUMMARY OF THE INVENTION With the foregoing considerations in mind, thepresent invention envisions a process and apparatus for dispensing ahardenable liquid and for treating such liquid in a manner to avoidhardening of the liquid within the apparatus during periods of disuse ofthe apparatus. Thus, a supply of liquid to be dispensed is housed withinan enclosed vessel. Pressurized air or gas introduced into the vesselforces the liquid through a discharge line, preferably under the controlof a dispensing valve. When the dispensing operation is discontinued forany substantial period, the pressurizing means is deactivated and inlieu thereof the air or gas is evacuated from the vessel by suitableevacuating means in a manner to withdraw the liquid back through thedischarge line into the vessel and, optionally, then maintain acontinuing reverse flow of air from the atmosphere through the dischargeline in a manner such that the air is introduced into the liquid at asubmerged location to bubble up through the liquid in intimate contactwith it. In this optional operation, curing or hardening of theabovedescribed anaerobic compositions can be prevented.

In a modified version, the pressurizing air or means also is introducedinto the liquid at a submerged location so that it, too, bubblesupwardly through the liquid and serves to prevent the curing thereof. Inthis form of the invention, in order to maintain a constant flow ofpressurizing air upwardly through the liquid, a certain amount of theair or gas is permitted to escape from the vessel as, for instance,through a conventional overpressure release valve.

BRIEF DESCRIPTION OF THE DRAWINGS To promote an understanding of theinvention, reference will now be made to the preferred embodimenttogether with a modification thereof illustrated in the accompanyingdrawing, and specific language will be used to describe the same. Itwill nevertheless be appreciated that no limitation of the scope of theinvention is thereby intended, such further modifications andalterations being contemplated as would normally occur to one skilled inthe art to which the invention relates.

Thus, in the accompanying drawings:

FIG. 1 is a diagrammatic view of the preferred embodiment of theinvention, and

FIG. 2 is a further diagrammatic view of a slightly modified embodimentof the invention.

DETAILED DESCRIPTION Referring now in detail to the accompanyingdrawings, and first considering the apparatus which is illustrateddiagrammatically in FIG. I, this apparatus includes a hermeticallysealed vessel 10 of any suitable construction having a removable coveror lid 12 and adapted to contain a supply of the hardenable liquid 14 tobe dispensed. The liquid preferably is housed within an inner container16 which here is shown as resting on the bottom of the vessel 10.

A liquid discharge line 18 extends in sealed relation through the coveror lid 12 and has an intake end 20 submerged in the liquid adjacent thebottom of the container 16 to define a discharge port for the liquid.The discharge line 18 preferably terminates at its outer end in asuitable nozzle 22 defining a discharge orifice and preferably under thecontrol of a conventional valve 23 which may be either manually orautomatically operable to permit application of a desired quantity ofthe hardenable liquid to a workpiece.

Communicating with the interior of the vessel through a supply line 24,is a suitable source 26 of pressurized air. It will be noted that theline 24 extends in sealed relation through a sidewall of the vessel 10at a location which, in the present instance, is opposite the innercontainer 16. However, the inner container 16 is spaced from thesidewall of vessel 10 to provide an airspace or a passage 28 so that theinflowing air may rise or pass upwardly into the top of the containerand exert a downward pressure on the surface of the liquid 14 within theinner container 16.

The pressure of the inflowing air is normally regulated in the preferredembodiment by a conventional reduction or regulating valve 30 interposedin the supply line 24. For controlling the admission of pressurized airinto the vessel 10, a further selectively operable valve 32 is disposedin the supply line 24 between the air pressure regulator 30 and thevessel 10.

The above-described pressurized air source 26 and its associated airsupply line 24 constitute a pressurizing means for maintaining a supplyof air at super atmospheric pressure within the vessel 10 above thesurface of the liquid 14 therein, whereby to discharge the liquid 14through the discharge line 18 and into the atmosphere through thedispensing nozzle 22 under the control of the dispensing valve 23.

It will be appreciated that in normal operating conditions when thevessel 10 is pressurized for dispensing purposes, the dispensing valve23 will be intermittently opened to discharge a predetermined amount ofthe liquid into successive work pieces. In this connection, it will bereadily apparent that the work pieces may be successively conveyed pastthe applicator nozzle 22 at regular time intervals, in which event thedispensing valve 23 may be automatically operated in timed relation tothe movement of the work pieces to apply an appropriate amount of liquidto each in succession. For this purpose the valve 23, nozzle 22 andassociated operating and control means, therefor, may be constructed andfunction in the manner disclosed in the US. Pat. No. 3,385,261 toWittemann et al., ofMay 28, 1968.

When the liquid dispensing function is discontinued for any appreciableperiod of time, there will be a tendency for the liquid contained withinthe discharge line 18, dispensing nozzle 22 and valve 23, to cure orharden. In order to prevent such curing during periods of nonuse, it isa particular feature of the present invention to associate evacuatingmeans with the vessel 10 in such a manner as to create and maintain asubatmospheric pressure therein. During the maintenance of suchsubatmospheric or negative pressure, so long as the dispensing valve 23is maintained open, there will be created a suction through the supplyline 18, causing first a withdrawal of the hardenable liquid in areverse flow direction backwardly through the nozzle 22, valve 23 andline 18, into the container 16, following which the continued operationof the evacuating means will maintain a reverse flow of air from theatmosphere through the same parts and into the lower portion of thecontainer 16 through the submerged end of the discharge line 18. The airthus entering the liquid 14 beneath this surface will bubble upwardlythrough the liquid and contact the liquid substantially throughout itsdepth. When liquid 14 is an anaerobic sealant or other liquid stabilizedby contact with air, this flow will retard or prevent its curing withinthe container 16.

A suitable exemplification of the evacuating means may be as illustratedin FIG. 1, consisting of a conventional aspirator 35 which utilizes aflow of compressed or pressurized air through a constriction 34 in anair bypass line 36 to induce the withdrawal or evacuation of air throughlines 24 and evacua' tion line 38 from the interior of the vessel 10.

It will be noted that the evacuation line 38 communicates with thebypass line 36 at its constriction 34, whereby the flow of pressurizedair through the line 36 at constriction 34 will induce a flow of airthrough evacuation line 38 into the constriction, the air beingdischarged into the atmosphere through the open end 40 of the bypassline or otherwise disposed of.

In order to render the pressurizing means and the evacuating meansselectively and alternately operable, there may be employed suitablylocated valves such as the valve 32 earlier described, as well as thevalve 42, interposed in the bypass line 36, and the valve 44 interposedin the evacuation line 38.

The bypass line 36 communicates with the air supply line 24 at alocation between the pressure regulator 30 and the shutoff valve 32 forthe supply line. Thus, when the shutoff valve 32 is closed, todiscontinue the supply of pressurized air into the vessel 10, if at thesame time the bypass valve 42 is opened, the supply of pressurized airwill be diverted from the line 24 into and through the bypass line 36and its constriction 34. Opening of the control valve 44 for theevacuation line 38 will at this time result in an induced withdrawal ofair from the vessel 10 through lines 24 and 38 and the constriction 34to be discharged at 40 with the main or primary airflow through the line36.

In the overall operation of the apparatus, exemplified in FIG. 1, whenit is desired to dispense the hardenable liquid through the dispensingnozzle 22, the valves 42 and 44 are closed to prevent any escape of airfrom the supply line 24 through lines 36 and 38. At the same time, thevalve 32 is opened and air from the pressurized air supply 26 is thusadmitted through the supply line 24 to the interior of the vessel 20where its pressure is imposed upon the surface of the liquid 14. Theair, being at superatmospheric pressure, urges the liquid into theintake port 20 at the lower end of the liquid discharge line 18. Openingof the dispensing valve 23 will permit the liquid to flow through theline and be discharged through the nozzle 22 onto a workpiece. Closingof the valve 23 will discontinue the discharge of liquid to nozzle 22.Normally the valve 23 will be intermittently opened to permitapplication of a predetermined amount of liquid to each of a successionof workpieces moving past the nozzle 22.

When dispensing of the hardenable liquid is to be discontinued for anyappreciable period of time, the valve 32 will be closed to discontinuethe flow of pressurized air into the vessel 10. Also the waves 42 and 44will be opened to permit a flow of pressurized air from the line 24through the bypass line and aspirator 36 and 35, respectively, thusinducing an evacuation of air from the vessel 10 through the lines 24and 38 and the aspirator 35. After evacuation, dispensing valve 23 willbe opened. The resulting creation and maintenance of subatmosphericpressure within the vessel 10 will cause first a backflow of thehardenable liquid through the nozzle 22, dispensing valve 23 anddischarge line 18 into the receptacle or container 16, following whichthere will be maintained a continuous backflow of air from theatmosphere through these same parts and into the liquid 14 through thesubmerged intake end or port 20 of the discharge line 18. Such air willthen bubble upwardly through the liquid en route to the line 24, 38 andthe aspirator 35.

in the modification illustrated diagrammatically in FIG. 2, theconstruction and mode of operation are substantially similar to thosedisclosed in connection with FIG. 1, except that the air delivered intothe vessel for the purpose of expelling the liquid 14, is delivered at alocation submerged beneath the surface of liquid so that the air bubblesupwardly through the liquid in the same manner and for the same purposeas does the backflowing air through the discharge line when thecontainer and the discharge line are evacuated in the precedingembodiment.

As in the preceding embodiment, the hardenable liquid 14 may beconveniently held within a disposable container 16 which, in turn, ishoused within the fluidtight vessel [00 having a removable fluidtightcover 120.

In this embodiment, a flow of air from a suitable source of pressuresuch as a pump 260 is delivered through a supply line 240 disposed influidtight manner through the cover and has its delivery end 242depending substantially beneath the surface of the liquid to dischargethe incoming pressurized air at a location substantially submergedbeneath the surface of the liquid and substantially adjacent to thebottom of the container 16. In order that there may be a continuing flowof pressurizing air into the liquid to bubble upwardly therethrough andthus maintain the liquid in contact with the oxygen in the air, thecontainer may conveniently be equipped with a pressure relief valve 244,set to release the air at a pressure which is slightly lower than thepressure of air passing through a pressure regulator 300 interposed inthe air supply line 240.

As in the preceding embodiment, a valve 320 is interposed in the supplyline 240 between the pressure regulator 300 and the vessel 100 toprovide for shutting off the flow of air into the vessel when it isdesired to discontinue the dispensing operation.

The bypass line 360 in this arrangement communicates with the supplyline 240 of the pressurizing means between the pressure regulator 300and the valve 320 and itself is controlled by a shutoff valve 420. Whenthe air supply control valve 320 is closed, and the valve 420 is opened,the pressurized air will be caused to flow through the bypass line 360to and through the constriction 340 of the aspirator 350. Thus anegative pressure or suction is induced through the evacuation line 380which establishes communication between the constriction 340 of line 360and the interior of the vessel 100 at a location above the surface ofthe liquid 14 therein. A valve 440 in the line 380 will normally beclosed when the vessel 100 is pressurized to prevent loss of pressuretherefrom, but is opened during the evacuation of the vessel to permitair to be drawn upwardly and expelled through the aspirator 350.

As in the first embodiment, the pressurized liquid is discharged througha discharge line 180 having its intake end submerged in the liquid nearthe bottom of the container 16. The line 180 extends in sealed relationthrough the container cover 120 and terminates in a dispensing nozzle220 through which the hardenable liquid is dispensed under the controlof a valve 230. The operation of this embodiment is similar to that ofthe preceding embodiment except that during the dispensing operation,the inflow of pressurizing air through line 240 is injected into theliquid 14 at a submerged location beneath its surface and then bubblesupwardly in a generally constant flow for discharge through the pressurerelief valve 244 into the atmosphere. Such movement of air through theliquid inhibits hardening during use of the apparatus. As before, thepressurized liquid is dispensed through the discharge line 180 andnozzle 220 under the control of the valve 230.

When a dispensing operation is discontinued for any appreciable lengthof time, the flow of air into the liquid is discontinued by shutting offthe valve 320. The alternatively operable evacuating means is thenrendered operative by opening the valve 420 to permit diversion of thepressurized air from the line 240 through the line 360. At the sametime, the normally closed valve 440 is opened so that the air may beevacuated from the vessel 100 through the line 380 and constriction 340of the aspirator for discharge into the atmosphere.

So long as the evacuating means is thus operated, the dispensing valve230 of the discharge line 180 is maintained open. Thus, there isproduced a backflow of the liquid from the nozzle 220, valve 230 andline 180 into the container, following which there is a continuingbackflow of atmospheric air through these same ports and into thecontainer to again produce a flow of air upwardly through the hardenableliquid 14. When liquid 14 is stabilized by the presence of air, thisflow will prevent the liquid from curing or hardening, pendingresumption of the dispensing operation.

As has been explained above, the dispensing devices described herein areparticularly adaptable to use with anaerobic compositions and extremelyimportant benefits can be obtained thereby. Such use of these devicesmakes availa ble a process for applying anaerobic compositions whichclearly is superior to prior art processes. As explained above,anaerobic compositions are mixtures of a polymerizable acrylate esterand a hydroperoxide catalyst therefor, which harden by a polymerizationprocess which is inhibited by the presence of oxygen. As long as thepressure within the sealed vessel is maintained by compressed gasses, atleast a portion of which is oxygen, the hardening reaction is eliminatedor inhibited suffi-' ciently to make the anaerobic sealants andadhesives particularly adaptable to use in the devices disclosed herein.Since the polymerization does not take place to any significant extent,the viscosity of the anaerobic composition remains substantiallyconstant, thus making the dispensing of uniform quantities of theanaerobic composition relatively easy.

Having thus described the invention, we claim:

1. Apparatus for dispensing a hardenable liquid which comprises: afluidtight vessel having therein a supply of said liquid to bedispensed, said liquid having an upper surface exposed to the pressureof gas within the vessel; at least one discharge line for conveying theliquid from the vessel to a point of discharge externally of the vessel,said discharge line having an intake end within the vessel submerged inthe liquid; selectively operable means for introducing gas into thevessel at a sufficient pressure to discharge the liquid from the vesselthrough said discharge line; and a cleaning system, including means fordiscontinuing the introduction of gas into the vessel and means forcausing a backflow of atmospheric air completely through said line toits intake end.

2. Apparatus as defined in claim 1, wherein said last mentioned meansevacuates air from said vessel to withdraw the liquid from saiddischarge line back into the vessel.

3. Apparatus as defined in claim 1, including valve means associatedwith said discharge line for controlling the discharge of liquidtherethrough.

4. Apparatus for dispensing a hardenable liquid which comprises: afluidtight vessel having therein a supply of said liquid to bedispensed, said liquid having an upper surface exposed to the pressureof gas within the vessel; at least one discharge line for conveying theliquid from the vessel to a point of discharge externally of the vessel,said discharge line having an intake end within the vessel submerged inthe liquid, selectively operable means for introducing gas into thevessel at a sufiicient pressure to discharge the liquid from the vesselthrough said discharge line; and a cleaning system, including means fordiscontinuing the introduction of gas into the vessel and means forcausing a backflow of liquid and atmospheric air through said line, saidlast mentioned means comprising evacuating means communicating with thevessel and applying a subatmospheric pressure to the surface of theliquid whereby to cause a backflow of fluid through said line into thevessel and thereafter to produce a backflow of atmospheric air throughthe line and through the submerged intake end of the said dischargeline, whereby to produce a bubbling of air upwardly through the liquid.

5. Apparatus as defined in claim 4, wherein said evacuating meanscomprises an aspirator, means for supplying a primary flow ofpressurized air through said aspirator, and an evacuation line extendingfrom said vessel through the aspirator and in aspirating relation tosaid primary airflow.

6. Apparatus for dispensing a hardenable liquid comprising ahermetically sealed vessel for containing a supply of the liquid to bedispensed; a discharge line extending between the interior of saidvessel and the atmosphere and having an intake end communicating withthe interior of said vessel at a location substantially below the levelof said liquid; selectively operable pressurizing means for maintaininga supply of air at superatmospheric pressure within said vessel abovethe surface of said liquid, whereby to discharge said liquid from thevessel into the atmosphere; means for discontinuing said pressurized airsupply, and evacuating means operable during discontinuance of said airsupply to evacuate air from the vessel whereby to withdraw liquid fromsaid discharge line back into the vessel and then to maintain a reverseflow of air from the atmosphere through said discharge line upwardlythrough the liquid.

7. Apparatus as defined in claim 6, wherein said pressurizing meansincludes an air supply line having a delivery end communicating with thevessel at a location submerged in the liquid substantially below theupper surface thereof, whereby the inflowing air bubbles upwardlythrough the liquid; said evacuating means including an evacuation linehaving an intake end in communication with the interior of the vessel.

8. Apparatus as defined in claim '7, including a dispensing valve forcontrolling the passage of liquid through said discharge line.

9. The process of dispensing an anaerobic liquid from a completelyenclosed and sealed container through a discharge line leading from saidcontainer to the atmosphere and having an intake port within thecontainer below the level of said liquid, comprising the steps ofintroducing air at superatmospheric pressure into said container abovethe liquid to discharge the said liquid through the discharge line;discontinuing said supply of air; then evacuating the air from abovesaid liquid to maintain a subatmospheric pressure within the container,thus sucking the liquid back through the line into the container andthereafter maintaining an influx of atmospheric air into the containerbelow the liquid level to bubble upwardly through the liquid, whereby toprevent curing of the anaerobic liquid.

10. The process defined in claim 9, including the step of introducingthe superatmospheric air into the container at a location submerged inthe liquid, thereby causing said air to bubble upwardly through theliquid to prevent curing of the latter

2. Apparatus as defined in claim 1, wherein said last mentIoned meansevacuates air from said vessel to withdraw the liquid from saiddischarge line back into the vessel.
 3. Apparatus as defined in claim 1,including valve means associated with said discharge line forcontrolling the discharge of liquid therethrough.
 4. Apparatus fordispensing a hardenable liquid which comprises: a fluidtight vesselhaving therein a supply of said liquid to be dispensed, said liquidhaving an upper surface exposed to the pressure of gas within thevessel; at least one discharge line for conveying the liquid from thevessel to a point of discharge externally of the vessel, said dischargeline having an intake end within the vessel submerged in the liquid,selectively operable means for introducing gas into the vessel at asufficient pressure to discharge the liquid from the vessel through saiddischarge line; and a cleaning system, including means for discontinuingthe introduction of gas into the vessel and means for causing a backflowof liquid and atmospheric air through said line, said last mentionedmeans comprising evacuating means communicating with the vessel andapplying a subatmospheric pressure to the surface of the liquid wherebyto cause a backflow of fluid through said line into the vessel andthereafter to produce a backflow of atmospheric air through the line andthrough the submerged intake end of the said discharge line, whereby toproduce a bubbling of air upwardly through the liquid.
 5. Apparatus asdefined in claim 4, wherein said evacuating means comprises anaspirator, means for supplying a primary flow of pressurized air throughsaid aspirator, and an evacuation line extending from said vesselthrough the aspirator and in aspirating relation to said primaryairflow.
 6. Apparatus for dispensing a hardenable liquid comprising ahermetically sealed vessel for containing a supply of the liquid to bedispensed; a discharge line extending between the interior of saidvessel and the atmosphere and having an intake end communicating withthe interior of said vessel at a location substantially below the levelof said liquid; selectively operable pressurizing means for maintaininga supply of air at superatmospheric pressure within said vessel abovethe surface of said liquid, whereby to discharge said liquid from thevessel into the atmosphere; means for discontinuing said pressurized airsupply, and evacuating means operable during discontinuance of said airsupply to evacuate air from the vessel whereby to withdraw liquid fromsaid discharge line back into the vessel and then to maintain a reverseflow of air from the atmosphere through said discharge line upwardlythrough the liquid.
 7. Apparatus as defined in claim 6, wherein saidpressurizing means includes an air supply line having a delivery endcommunicating with the vessel at a location submerged in the liquidsubstantially below the upper surface thereof, whereby the inflowing airbubbles upwardly through the liquid; said evacuating means including anevacuation line having an intake end in communication with the interiorof the vessel.
 8. Apparatus as defined in claim 7, including adispensing valve for controlling the passage of liquid through saiddischarge line.
 9. The process of dispensing an anaerobic liquid from acompletely enclosed and sealed container through a discharge lineleading from said container to the atmosphere and having an intake portwithin the container below the level of said liquid, comprising thesteps of introducing air at superatmospheric pressure into saidcontainer above the liquid to discharge the said liquid through thedischarge line; discontinuing said supply of air; then evacuating theair from above said liquid to maintain a subatmospheric pressure withinthe container, thus sucking the liquid back through the line into thecontainer and thereafter maintaining an influx of atmospheric air intothe container below the liquid level to bubble upwardly through theliquid, whereby to prevent curing of the anaerobic liquid.
 10. Theprocess defined in claim 9, including the step of introducing thesuperatmospheric air into the container at a location submerged in theliquid, thereby causing said air to bubble upwardly through the liquidto prevent curing of the latter.